This invention relates generally to pressure extraction pumping systems for recovering liquid hydrocarbons from ground water, and more particularly concerns a pressure extraction pump system which can be used to skim free floating hydrocarbon liquid from ground water in a well bore.
At petroleum handling facilities such as refineries, storage facilities, terminal facilities, and gasoline stations, spillage of liquid hydrocarbons can result in the contamination of ground water in the immediate vicinity. The problem of ground water contamination can occur as a result of slow leakage over time or a more catastrophic spillage event. In either case, the liquid hydrocarbons seep through the ground to the ground water table level. Because liquid hydrocarbons have specific gravities that are less than water and are generally immiscible with water, they form a layer on top of the ground water table.
Conventionally, in order to remove the contaminating liquid hydrocarbons from the ground water, it has been necessary to drill a number of bore holes in the area where the contamination exists and then pump large quantities of ground water out of the bore holes to create a cone of depression in the ground water table adjacent each of the well bores. Gravity forces the liquid hydrocarbons to flow toward the center of the cones of depression, and the liquid hydrocarbons callect there within each bore. In some areas where the aquifer is particularly prolific, it may be necessary to pump very large quantities of ground water before even a shallow cone of depression can be created. Moreover, in tidal areas, the rise and fall of the tiedes may, within the context of a prolific aquifer, make it impossible to achieve a stationary cone of depression no matter how much ground water is pumped to the surface.
Conventionally, it is known that the deeper the cone of depression, the thicker the free floating layer of liquid hydrocarbons will be on top of the ground water at the center of the cone of depression. A thick layer of liquid hydrocarbons facilitates recovery of the liquid hydrocarbons with a minimum amount of water. Obviously, where a prolific aquifer exists, the cone of depression will necessarily be shallow, the layer of free floating liquid hydrocarbons will be thin, and a large amount of ground water will have to be pumped to the surface as a percentage of the free floating liquid hydrocarbons that are removed. The more ground water that is pumped to the surface, the greater the expense is in separating the liquid hydrocarbons from the ground water.
In connection with a catastrophic spill, the spill forms a dispersion dome from the point of the spill generally expanding outward into a cone of descent toward the static water table. Within time, the liquid hydrocarbons begin to settle onto the existing static water table and begin to depress it forming a layer of liquid hydrocarbons below the point of spill within the expanded cone of descent. If a bore is made at the point of spill, the liquid that collects in the well bore will have a fairly thick layer of liquid hydrocarbons. In order to exploit the fact that the liquid hydrocarbons are in a somewhat concentrated area beneath the point of the spill, and before the liquid hydrocarbons have dispersed due to their own hydraulic head and general ground water flow, it is advantageous to pump as much of the liquid hydrocarbon out of the well bore as soon as possible. Early removal of the concentrated liquid hydrocarbons reduces the hydraulic head of liquid hydrocarbons and helps minimize the lateral spreading of the contamination.
Normally where ground water clean up is to be undertaken it is necessary to acquire permits from environment protection agencies before the decontaminated ground water can be discharged from the site. In most spillage cases where the public health and safety are not immediately effected, there may be administrative delays in acquiring such permits and until such permits are acquired, any water that is pumped to the surface must be stored or trucked away to an approved disposal treatment site until such time as the requisite permit to discharge the ground water has been acquired. It is therefore important, during the early phase of a clean up of a catastrophic spill, while the liquid hydrocarbons remain concentrated beneath the spill and when no discharge permit is available, that the minimum amount of ground water as a percentage of the liquid hydrocarbons be pumped to the surface. In order to exploit the situation, it is necessary that the intake of the pump be located within the liquid hydrocarbon layer so that the smallest amount of ground water is pumped to the surface.
While the prior art indicates an understanding that it is important to locate the pump intake at the level of the liquid hydrocarbon layer, achieving that result, as a practical matter, is very difficult, McLaughlin et al. U.S. Pat. No. 4,527,633 discloses a pump which has a separate inlet for the pump vessel which inlet is attached to a float and rides up and down on the water table along the cable. The inlet is connected to a flexible tubing which is in turn connected to the vessel pump chamber. The pressure that forces the liquid hydrocarbons into the inlet is limited by the amount of the liquid hydrocarbons existing above the opening to the inlet. If the float rides high in the liquid hydrocarbons, the head is reduced, and the time required to fill the pump vessel is increased. Moreover, within a tidal area where the water table may vary as much as two feet or more during the course of a 24 hour period, the flexible tubing attached to the inlet would not accommodate such changes in the water table.
In addition to collecting as much of the liquid hydrocarbon as possible as a percentage of the ground water, it is also important that the pump operate as efficiently as possible. In that regard, where extraction pressure pumps such as those shown in the McLaughlin et al. are used, the pump operates by allowing the fluid in the well bore to enter the pump vessel through an inlet under the static head pressure of the liquid in the bore. Once the vessel has filled, either as a function of time or as a function of a sensed level of liquid in the vessel, the vessel is pressurized by means of compressed gas pumped from the surface. The compressed gas forces the intake valves closed and then forces the fluid in the pump vessel to the surface. In order to pump efficiently, it is necessary that the top intake valve close even before the vessel is pressurized so that the rising head of liquid in the well bore and the pressurizing air do not force the free floating liquid hydrocarbons out of the top intake valve. Closing the top intake valve once the vessel is filled not only minimizes the loss of liquid hydrocarbons during each pumping cycle but also minimizes turbulence which tends to emulsify and mix the liquid hydrocarbons with the ground water resulting in greater costs in the ultimate separation process at the surface. Also the valve open area to receive fluids must be maximized as a percent of the extraction vessel's body diameter.